Embodiments of the inventive concepts disclosed herein relate to substrate guided displays including but not limited to head up displays (HUDs), such as, fixed HUDs and worn displays (e.g., head worn displays, helmet mounted displays, virtual glasses, etc.).
HUDs provide significant safety and operational benefits including precise energy management and conformal flight paths. These safety and operational benefits are enjoyed by operators of air transport aircraft, military aircraft, regional aircraft and high end business jets where HUDs are generally employed. These safety and operational benefits are also desirable in smaller aircraft.
Conventional HUDs are generally large, expensive and difficult to fit into smaller aircraft, such as, business and regional jets as well as general aviation airplanes. Often, conventional HUDs rely on large optical components to form adequate field of view and viewing eye box. The large optical components are often associated with collimating or non-collimating projectors and include lens, prisms, mirrors, etc. The volume of the packages including the optical components of the HUD is too large to fit within the constrained space in the cockpit of smaller aircraft. Further, conventional HUDs rely upon optical components which are generally too expensive for the cost requirements of smaller aircraft and worn displays.
Substrate guided HUDs have been proposed which use waveguide technology with diffraction gratings to preserve eye box size while reducing size of the HUD. U.S. Pat. No. 4,309,070 issued St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose substrate waveguide HUDs. U.S. Pat. No. 8,634,139 discloses a catadioptric collimator for HUDs. The U.S. patent applications listed in the Cross Reference to Related Applications above disclose compact head up displays (HUDS) and near eye displays using multiple gratings, multiple waveguides, and/or multiple waveguide layers for pupil expansion.
It is desirous to make the projector for waveguide HUDs in a compact arrangement. Aligning optical components in small projector implementations can be difficult especially as sizes are minimized. Folded paths used in conventional projectors can require optical components that add to the package size for the projector. Projectors also often require a corrector lens which can be expensive and add to size of the collimator.
Pupil expansion using multiple layers or multiple waveguides with input and output diffraction gratings adds to the complexity of the waveguide display. For example, pupil expansion using multiple layers, multiple waveguides, and/or multiple gratings can add to the size, weight and cost of the display and can reduce the brightness and contrast of the display. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can be glossy due to air gaps and the number of gratings. The air gaps can induce geometric coupling losses. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can add haze to the final image.